The mysterious gap inside Grid

Question

There's this gap inside Grid which I cannot seem to remove. Perhaps someone knows how.

blocks = Table[{Graphics[{Darker@Green, Rectangle[{0, 0}, {1000, 200}]}]}, {i, 6}]
myGrid = Grid[blocks, Spacings -> {0, 0}, Frame -> All]

All nice and even at 100% zoom. Now if I zoom in on this to say 640% inside the notebook:

Extra space appears below each item as shown. The orange box received by clicking on the graphics suggests that Grid is responsible for the gap but Spacings have already been set to 0. Ssing Magnify will also cause the issue to appear at lower zoom rates. Does anyone know a fix for this in Grid? Or do I have to resort to GraphicsGrid which doesn't have this issue.

EDIT: This is the result produced from using the code as provided by Mike's answer (copy and pasted). And this one with it magnified so the code can be included in the screenshot.

I'm going to re-emphasize that this issue only occurs when I zoom in far enough or use Magnify.

Edit2: I'm on Mathematica 9.0.0

Answer 1

I can reproduce the problem described by OP in Mathematica 9.0.1 on Windows 8.1.

By using FrontEnd`UndocumentedBoxInformationPacket to check the displayed Boxes' layout in the FrontEnd, I wildly guess that the cause of the problem might be hiding in the FrontEnd layout engine (of only the Windows version maybe?). If it's true, then there might be nothing we users can do with it...

Here is my experiment and observation. I extracted the layout information and redrew them in a more clarified way (click image to see it larger; the code is attached afterward). In the screenshot, the upper green grid and the left column in this panel are corresponding to Grid, and the lower grid and the right column are to GraphicsGrid:

blocks = Table[{Graphics[{Darker@Green, Rectangle[{0, 0}, {1000, 200}]}, PlotRangePadding -> 0, PlotRangeClipping -> True, ImagePadding -> 0]}, {i, 2}];

myGrid      = Grid[blocks, Spacings -> {0, 0}, Frame -> All];
myGraphGrid = GraphicsGrid[blocks, Spacings -> {0, 0}, Frame -> All, PlotRangePadding -> 0];

gridNB      = myGrid // ToBoxes // Notebook[{Cell[BoxData[#], CellMargins -> 0, CellFrameMargins -> 0]}, ShowCellBracket -> False, Saveable -> False, WindowClickSelect -> False, Selectable -> False, WindowFrame -> "ThinFrame", WindowElements -> {}, WindowFrameElements -> {}, WindowMargins -> {{10, Automatic}, {Automatic, 10}}, WindowSize -> {200, 300}] & // NotebookPut;
graphGridNB = myGraphGrid // ToBoxes // Notebook[{Cell[BoxData[#], CellMargins -> 0, CellFrameMargins -> 0]}, ShowCellBracket -> False, Saveable -> False, WindowClickSelect -> False, Selectable -> False, WindowFrame -> "ThinFrame", WindowElements -> {}, WindowFrameElements -> {}, WindowMargins -> {{10, Automatic}, {Automatic, 320}}, WindowSize -> {200, 300}] & // NotebookPut;

{mgnf1, mgnf2} = 100 CurrentValue[#, Magnification] & /@ {gridNB, graphGridNB};
mgnfController1 = Row[{HorizontalGauge[Dynamic[mgnf1, (SetOptions[gridNB, Magnification :> #/100.]; mgnf1 = #) &], {10, 1000}], Style[Row[{Dynamic[mgnf1], "%"}], 20]}];
mgnfController2 = Row[{HorizontalGauge[Dynamic[mgnf2, (SetOptions[graphGridNB, Magnification :> #/100.]; mgnf2 = #) &], {10, 1000}], Style[Row[{Dynamic[mgnf2], "%"}], 20]}];

Clear[BRtoPolygon]
BRtoPolygon[boundingRect_, zCoord_: RandomReal[]] := Outer[List, ##] & @@ MapAt[Minus, boundingRect\[Transpose], 2] // MapAt[Reverse, #, 2] & // ArrayPad[Flatten[#, 1], {0, {0, 1}}, zCoord] & // Polygon

gridLayout = DynamicModule[{bips, layer, zCoordRule, hueRule},
            Dynamic[
                Module[{Graphics3DTemp, zCoord, hue},
                    bips = MathLink`CallFrontEnd[FrontEnd`UndocumentedBoxInformationPacket[#]] &[gridNB];
                    layer = bips //. {FE`BoxType -> bt_, FE`Position -> pos_, FE`BoundingRectangle -> br_, __, FE`Children -> chd_} :>
                                        {
                                            bt,
                                            If[And @@ (NumericQ /@ Flatten[{pos, br}]), 
                                                Function[{pts, zCoord}, 
                                                        Graphics3DTemp[{
                                                                        FaceForm[Hue[hue, .1, 1]], EdgeForm[Hue[hue, 1, .7]], BRtoPolygon[pts, zCoord], 
                                                                        If[MemberQ[{"GridBox", "GraphicsBox", "RectangleBox"},bt],
                                                                           Text[Style[bt, 15], Append[{1, -1} Last[pts], zCoord]], {}]
                                                                       }]
                                                        ][pos + # & /@ br, zCoord],
                                                Hold[Sequence[]]],
                                            chd
                                        } /. {bt_String, Hold[Sequence[]], chd_} :> Hold[Sequence[]] // ReleaseHold;
                    zCoordRule = Map[Function[{pos}, pos -> (layer[[##]] & @@ pos /. zCoord -> Length[pos])], Position[layer, Graphics3DTemp[__]]];
                    hueRule = Thread[# -> Rescale[Range[Length@#]]] &@Position[layer, hue];
                    ReplacePart[ReplacePart[layer, zCoordRule], hueRule] /. Graphics3DTemp -> Graphics3D // Cases[#, g_Graphics3D :> g, ∞] & // Rest //
                        Show[#,
                                Axes -> True, AxesStyle -> Blue, AxesLabel -> (Style[#, 17, Italic, Blue, Bold] & /@ {"width", "height", "layer"}),
                                Boxed -> False, ViewVertical -> {-1, 0, 0}, ViewPoint -> 1000 {-.9, -1, .5}, 
                                BoxRatios -> {Automatic, Automatic, 400}, ImageSize -> 700, Lighting -> {{"Ambient", White}}] &
                    ],
                UpdateInterval -> 0]
            ];

graphGridLayout = DynamicModule[{bips, layer, zCoordRule, hueRule},
            Dynamic[
                Module[{Graphics3DTemp, zCoord, hue},
                    bips = MathLink`CallFrontEnd[FrontEnd`UndocumentedBoxInformationPacket[#]] &[graphGridNB];
                    layer = bips /. e : {FE`BoxType -> "InsetBox", FE`Position -> pos_, __, FE`Children -> {{FE`BoxType -> "GraphicsBox", __}}} :> ReplacePart[e, {6, 2, 1, 2, 2} -> pos] //.
                                    {FE`BoxType -> bt_, FE`Position -> pos_, FE`BoundingRectangle -> br_, __, FE`Children -> chd_} :>
                                        {
                                            bt,
                                            If[And @@ (NumericQ /@ Flatten[{pos, br}]), 
                                                Function[{pts, zCoord}, 
                                                        Graphics3DTemp[{
                                                                        FaceForm[Hue[hue, .2, 1]], EdgeForm[Hue[hue, 1, .7]], BRtoPolygon[pts, zCoord], 
                                                                        If[MemberQ[{"InsetBox", "GraphicsBox", "RectangleBox"}, bt],
                                                                           Text[Style[bt, 15], Append[{1, -1} First[pts], zCoord]], {}]
                                                                       }]
                                                        ][pos + # & /@ br, zCoord],
                                                Hold[Sequence[]]],
                                            chd
                                            } /. {bt_String, Hold[Sequence[]], chd_} :> Hold[Sequence[]] // ReleaseHold;
                    zCoordRule = Map[Function[{pos}, pos -> (layer[[##]] & @@ pos /. zCoord -> Length[pos] + Mean[pos[[1 ;; -1]]])], Position[layer, Graphics3DTemp[__]]];
                    hueRule = Thread[# -> Rescale[Range[Length@#]]] &@Position[layer, hue];
                    ReplacePart[ReplacePart[layer, zCoordRule], hueRule] /. Graphics3DTemp -> Graphics3D // Cases[#, g_Graphics3D :> g, ∞] & // Rest //
                        Show[#,
                                Axes -> True, AxesStyle -> Blue, AxesLabel -> (Style[#, 17, Italic, Blue, Bold] & /@ {"width", "height", "layer"}),
                                Boxed -> False, ViewVertical -> {-1, 0, 0}, ViewPoint -> 1000 {-.9, -1, .5}, 
                                BoxRatios -> {Automatic, Automatic, 700}, ImageSize -> 700, Lighting -> {{"Ambient", White}}] &
                    ],
                UpdateInterval -> 0]
            ];

panel = Grid[{{mgnfController1, mgnfController2},
              {gridLayout, graphGridLayout}},
             Frame -> All, Alignment -> {Left, Top}] // ToBoxes //
          Notebook[{Cell[BoxData[#], "Output", CellMargins -> 0, CellFrameMargins -> 0]}, ShowCellBracket -> False, Saveable -> False, WindowElements -> {}, WindowFrame -> "ThinFrame", WindowFrameElements -> {"CloseBox"}, WindowMargins -> {{220, Automatic}, {Automatic, 10}}, WindowSize -> All] & // NotebookPut;

Answer 2

I was able to reproduce the effect (in version 7 under Windows) but I don't yet fully understand it. Partly it appears when you have automatically-resizing Graphics objects contained in a Grid object that is wider than the Notebook window. For example, using this code:

blocks = Table[{Graphics[{Darker@Green, Rectangle[{0, 0}, {1000, 200}]}, 
     ImagePadding -> 0, PlotRangePadding -> 0]}, {i, 6}];

myGrid = Grid[blocks, Spacings -> {0, 0}, Frame -> All];

Style[myGrid, Magnification -> 3]

And in a Notebook window that is easily able to contain the Graphic I get a solid green area with only fine black dividers:

However, if I resize the Notebook window to a narrower-than-graphic size I see this:

However magnification also plays a role here. Using a fixed ImageSize, which prevents resizing, combined with magnification shows a gap even when the Notebook is plenty wide to contain it:

Style[
 myGrid /. g_Graphics :> Show[g, ImageSize -> 50],
 Magnification -> 4
]

Answer 3

Magnify 10 times or more, ...

The basic idea is to use a GraphicsGrid

blocks = Table[{Graphics[{Darker@Green, Rectangle[{0, 0}, {100, 20}]},
  ImagePadding -> None, PlotRangePadding -> None]}, {i, 6}]

myGrid = GraphicsGrid[blocks, Spacings -> Scaled@.0, Frame -> All]

The options differ slightly for GraphicsGrid, see DocumentationCenter

Edit1: More workarounds... Another approach is to "Rasterize" Graphics output or to "Pane" it

    blocks = Table[{Graphics[{Darker@Green, Rectangle[{0, 0}, {1, .2}]}, 
         ImagePadding -> None, PlotRangePadding -> None]}, {i, 6}] // 
      Map[Rasterize, #, {2}] &
    myGrid = Grid[blocks, Spacings -> {0, 0}, Frame -> All, 
      FrameStyle -> {Blue, AbsoluteThickness@3}]

    blocks = Table[{Graphics[{Darker@Green, Rectangle[{0, 0}, {1, .2}]}, 
         ImagePadding -> None, PlotRangePadding -> None]}, {i, 6}] // 
      Map[Pane, #, {2}] &
    myGrid = Grid[blocks, Spacings -> {0, 0}, Frame -> All, 
      FrameStyle -> {Blue, AbsoluteThickness@3}]

In simple cases setting grid's "Background" to Darker@Green is an acceptable workaround.

Answer 4

blocks = Table[{Graphics[{Darker@Green, 
     Rectangle[{0, 0}, {1000, 200}]}, PlotRangePadding -> 0, 
    ImagePadding -> 0]}, {i, 6}]
myGrid = Grid[blocks, Spacings -> {0, 0}, Frame -> All]

If you are still seeing whitespace as per your comment then please post a pic and the exact code that you used.

Edit

As per reply to Mr Wizard. At the max (max of widow element) magnification of 300% I get

Using Magnify of 6 (600%) I still do not see a problem:

I'm on OS X 10.9.4 and Mma 9.0.1

Answer 5

I did my investigations with V9.0.1 running on OS X. My findings may be (probably are) platform dependent.

First I eliminated the framing from the problem space by writing this code.

blocks =
  With[{size = {5, 1}},
    Table[
      Graphics[{
        {EdgeForm[Black], FaceForm[Transparent], Rectangle[{0, 0}, size]},
        {Darker@Green, 
           Scale[Rectangle[{0, 0}, size], .95 {1., 1. - size[[2]]/size[[1]]}]}},
        PlotRangePadding -> None],
      {2}]];

This gives good results over a wide range of magnifications.

Magnify[Column[blocks, Spacings -> -.14], 1/2]

Magnify[Column[blocks, Spacings -> -.14], 3]

I actually got good results with magnifications up to 5.

However, when I tried a magnification of 6.4, I ran into the same problem that the question demonstrates. I could find no setting for Spacings that removed the gap between the blocks. Instead, the rendering engine start to eat up the lower block and I made the spacing more negative. The window capture below shows this.

Magnify isn't the only source of trouble. Look what happen when I shrink the notebook window.